The present invention relates to a charged particle beam scan and irradiation method, charged particle beam apparatus, workpiece observation method and workpiece processing method.
When an insulator workpiece is observed or processed by a charged particle beam, such as an ion beam or electron beam (hereinafter also simply referred to as “beam”), the irradiation beam is raster scanned and positioned on the workpiece. Raster scanning is how to sequentially irradiate an array of points. Conventionally, to achieve good observed images and process results, the scanning order in raster scanning is skillfully modified into, for example, a thinned-out scanning order (scanning at an interval formed of a predetermined number of pixels) (see, for example, JP-B-6-38329). The thinning-out scanning order solves a problem of a charging effect resulting from ion beam irradiation, that is, secondary ions emitted from a mask are not successfully detected. FIG. 8 shows the scanning order of raster scan-based thinned-out scanning. In the following description, the left-to-right direction is the X direction and the up-to-down direction is the Y direction. The numbers in some of the pixels indicate the beam irradiation order. A pixel used herein is a unit area for single beam irradiation and an area divided in the X (horizontal) and Y (vertical) directions at an interval corresponding to a minimum unit of irradiation beam deflection. As shown in the figure, in the raster scan-based thinned-out scanning, a scan area is divided into pixels and for a certain row of pixels, the charged particle beam is applied to the center positions of pixels spaced apart by a predetermined number of pixels in the X direction. Once the beam irradiation is completed for that one row, the beam irradiation is repeated again at the interval formed of the predetermined number of pixels in the X direction for a row spaced apart by a predetermined number of lines (pixels) in the Y direction. As shown in the flowchart in FIG. 9, in raster scanning, after beam irradiation positions are determined for a certain row, beam irradiation is turned on, and once the irradiation for that one row is completed, the beam irradiation is temporarily turned off. Then, beam irradiation positions are determined for the next row to be scanned and the beam irradiation is turned on again for beam irradiation. This procedure is repeated to apply the beam to the scan area until the process is completed. Turning beam irradiation off herein used means that the beam is blanked before it reaches the workpiece so that the beam does not reach the workpiece. Turning beam irradiation on herein used means that the beam is not blanked but applied to the workpiece. On the other hand, for forming a patterned film on a workpiece surface by spraying a compound gas from a gas gun onto the workpiece and applying a focused ion beam on the workpiece surface with the compound deposited thereon, a method for improving patterned film formation efficiency is disclosed, in which an ion beam irradiation optical system is provided with means for digitally scanning the ion beam and the digital scanning means scans the ion beam at an interval greater than or equal to two pitches (see, for example, JP-A-1-293538).
In general, the contour of a process area of a workpiece does not always match with the boundary of pixels used in raster scanning. Therefore, to accurately process a process area that does not match with the boundary of pixels used in raster scanning, it is unfortunately required to specify the scan area such that it matches with the contour of the process area with sub-pixel accuracy. As described above, in raster scanning, since beam irradiation is temporarily turned off after beam irradiation is completed for a certain row and beam irradiation is turned on again to apply the beam to the next row in a repeated manner, the start position of charged particle beam irradiation matches with the contour of the process area. At the start position of beam irradiation, instability of the beam irradiation timing may cause process nonuniformity with respect to other positions. In particular, when the charged particle beam is applied to process the workpiece while a process gas, such as an etching gas or deposition gas, is sprayed to process positions, there is also a problem that the processed shape of the contour, which is the most important portion, is deteriorated.
On the other hand, in vector scanning, beam irradiation positions are specified with sub-pixel accuracy and a process area is scanned in a single stroke without interrupting beam irradiation. Although vector scanning can solve the above problem of raster scanning, the method for changing the scanning order, such as raster scan-based thinned-out scanning, cannot be applied without modification. As described above, to process a workpiece, the workpiece is irradiated with an irradiation beam while a process gas, such as an etching gas or deposition gas, is sprayed onto the workpiece. In a process using thinned-out scanning, as a scan line is scanned multiple times, the process gas that has been sprayed on the workpiece during the previous scans gets diffused in the process area. Therefore, the process gas can be effectively used in the process. On the other hand, in vector scanning, as beam irradiation is carried out before the process gas that has been sprayed onto the workpiece gets diffused into the next process position, there is a problem that the process gas that has been sprayed cannot be effectively used.
The invention has been made in view of such situations and aims to provide a charged particle beam scan and irradiation method, charged particle beam apparatus, workpiece observation method and workpiece processing method capable of improving contour line observation and process accuracy and effectively using a process gas sprayed on a workpiece during the process.